U.S. Pat. No. 5,047,913, which is assigned to the assignee of the present invention and is incorporated by reference herein, describes an auxiliary commutating circuit which is referred to as an auxiliary resonant commutation pole or phase leg (ARCP) circuit for enabling soft-switching, i.e., essentially zero-voltage switching (ZVS) of the main switching devices of a power converter and zero current switching (ZCS) of the auxiliary devices. The ARCP circuit comprises a pair of reversely poled electronic switching devices serially connected with an inductor and snubber capacitors, the inductor and capacitors forming a resonant circuit. The gating and conduction times of the switching devices of the ARCP circuit are controlled so as to establish essentially zero-voltage across the main switching devices of the converter when these latter devices are gated into conduction.
U.S. patent application Ser. No. 08/622,504, now abandoned describes an improvement in the ARCP circuit of U.S. Pat. No. 5,047,913, and, more particularly, to the controller associated with the ARCP switching devices to enhance efficiency, zero-voltage switching and fault tolerance. The disclosure of U.S. patent application Ser. No. 08/622,504 is hereby incorporated by reference. Notwithstanding the enhancements provided, the control circuit needed additional enhancement in order to be applied in high-power power conversion circuits, for example, converter circuits that operate in the range of 200 kilowatts and higher in which the dc link voltage is greater than about 500 volts and the ARCP phase leg current may be greater than 200 amperes. At such high levels of voltage and current, noise transients generated by high dv/dt and radiated electrical noise may be sufficient to disrupt the gate switching circuits. Accordingly, it is desirable to provide an ARCP circuit which has fault tolerance and noise immunity while operating at high power.